In general, this invention relates to apparatus for processing video signals. More particularly, this invention relates to apparatus for processing time division multiplex (TDM) video signals in which the signal durations of the TDM video signal are divisible by a common number greater than one to reduce circuit cost and complexity.
In the consumer video cassette recorder (VCR) field, it is common to separate the chrominance and luminance signals in a frequency fashion in order to eliminate time base errors which result in reproduced color inaccuracies. In addition, the bandwidths of the luminance and chrominance signals are usually limited in order to reduce the cost and complexity of the VCR equipment. However, the conventional "color-under" formats used in consumer VCRs have certain problems. First, the "color-under" amplitude modulated chrominance signal is subject to noise interference worsening the signal to noise ratio of the recorded signal. Moreover, the "color-under" chrominance signal is subject to errors in burst gating and regeneration of the color subcarrier frequency used in standard composite color video broadcast signals used in television sets. Moreover, the reduced bandwidth of both the chrominance and luminance component signals in the "color-under" format limits the use of such a format in a higher resolution, higher image quality mode which utilizes substantially the full bandwidths of the standard broadcast color video signal.
It has been proposed in commonly-assigned copending U.S. patent application Ser. No. 725,873, by Carl Schauffele, entitled VIDEO REPRODUCTION APPARATUS, to provide a bi-modal video cassette recorder which is selectively operable in a conventional "color-under" mode at reduced signal bandwidth and in a high resolution time-division-multiplex mode at greater signal bandwidth. As disclosed in this patent application, in the high resolution mode, both the luminance and chrominance components of a color video signal are recorded at substantially full broadcast bandwidths for increased image resolution. In addition, the luminance and chrominance components are recorded at separate times, therefore eliminating time base error problems which might result in color inaccuracies in a reproduced television picture. Since the entire TDM signal is modulated on a frequency modulated carrier, the difficulties encountered in the amplitude modulated "color-under" chrominance signal are eliminated and the signal to noise ratio for both the chrominance and luminance signals are increased.
In such a time division multiplex video signal recording and playback apparatus, there is a need to simplify the equipment circuitry and minimize the cost thereof. Since the video components of the TDM signal are sampled at a high frequency in order to compress the components into a single video line and in order to utilize the full component bandwidths, high speed counting circuitry is used for timing and control in processing the TDM signal.